that is the sum of the interior angles of a triangle,or the 3 sided polygons
the answer is x=24
by cross multiplying 4/5 and x/30, we get 5x= 120. divide 120 by 5, and you get 24.
rule: 400 + 25x
after month 12: 700 dollars
to start, we need to set a variable as the amount of months after you started your savings account. call this value x. now, we just have 25x as the amount you gain after x months, so the rule is 400 + 25x. to calculate how much you have after month 12, just plug in 12 to get 400 + 300 = 700 dollars.